In the case of the heavy metals Ag, As, Cd, Cr.
Cu. Hg, Pb, and Zn, we have found that there are ten categories
of consumption that are readily distinguishable in terms of their
different degrees of dissipation in use and different modes of
release to the environment. These are as follows:

1. Metallic uses, e.g. in alloys. Environmental
losses occur mainly in the production stage (discussed
previously) and as a result of corrosion in use or discharge to
landfills.

2. Plating and surface treatment (excluding
paints and pigments) generate some losses in the platings or
treatment process and some corrosion losses as above.

3. Paints and pigments generate losses at the
point of application and from weathering and wear. Some are
ultimately disposed of (e.g. in landfills) along with discarded
objects or building materials.

4. Batteries and electronic devices have
relatively short useful lives of 1-10 years. Production losses
can be significant. Most are discarded to landfills.

5. Other electrical equipment as above, but may
be longer-lived.

6. Industrial chemicals and reagents (e.g.
catalysts, solvents, etc.) not embodied in products have short
useful lives; catalysts and solvents are usually recycled, others
are lost directly to air or water.

8. Agricultural pesticides, fungicides and
herbicides are used dissipatively, on farms, nurseries, etc. Most
are immobilized by soil or biologically degraded and volatilized.
There is some uptake into the food chain and some amount of loss
via run-off.

9. Non-agricultural biocides include the above,
as used in homes and gardens, for termite control, etc. These
uses are dissipative but most biocides are immobilized by soil,
as above.

10. Pharmaceuticals, germicides, etc., are used
in the home or in healthservice facilities and are largely
discharged via sewage or to incinerators.

More detailed discussion of intermediate and
final uses of each metal can be found in the Appendix that
follows this chapter.

Table 8 Consumption-related emmissions factors
(ppm)

Metallic
usea

Plating
and
coatingb

Paint
pig-
mentsc

Electron
tubes
and ba-
-tteriesd

Other
electrical
equipmente

Chemical
uses, not
embodiedf

Chemica
uses, embodiedg

Agricul-
tural
usesh

Non-agri
cultural
usesi

Medi
cal
dentalj

Misc.
NEC

Silver

0.001

0.02

0.5

0.01

0.01

1

0.40

NA

NA

0.5

0.15

Arsenic

0.001

0

0.5

0.01

NA

NA

0.05

0.50

0.8

0.8

0.15

Cadmium

0.001

0.15

0.5

0.02

NA

1

0.15

NA

NA

NA

0.15

Chromium

0.001

0.02

0.5

NA

NA

1

0.05

NA

1

0.8

0.15

Copper

0.005

0

1.0

NA

0.10

1

0.05

0.05

1

NA

0.15

Mercury

0.050

0.05

0.8

0.20

NA

1

NA

0.80

0.9

0.2

0.50

Lead

0.005

0

0.5

0.01

NA

1

0.75

0.05

0.1

NA

0.15

Zinc

0.001

0.02

0.5

0.01

NA

1

0.15

0.05

0.1

0.8

0.15

a. As alloys or analgams (in the case of Hg)
not used in plating, electrical equipment, catalysts or dental
work. Losses can be assumed to be due primarily to wear and
corrosion, except for mercury which volatilizes.

b. Protective surfaces deposited by dip coating
(e.g. galvanizing, electroplating vacuum deposition, or chemical
bath (e.g. chromic acid). The processes in question generally
resulted in significant waterborne wastes until the 1970s.
Cadmium-plating processes were particularly inefficient until
recently (see discussion in Ayres et al., 1988, vol. II). Losses
in use are mainly due to wear and abrasion (e.g. silverplate), or
flaking (decorative chrome trim). In the case of mercury-tin
"silver" for mirrors, losses were largely due to
volatilization.

c. Paints and pigments are lost primarily by
weathering (e.g. for metal-protecting paints), by wear, or by
disposal of painted dyes or pigmented objects, such as magazines.
Copper- and mercury-based paints slowly volatilize over time. A
factor of 0.5 is rather arbitrarily assumed for all other paints
and pigments.

d. Includes all metals and chemicals (e.g.
phosphorus) in tubes and primary and secondary batteries, but
excludes copper wire. Losses in manufacturing may be significant.
Mercury in mercury vapour lamps can escape to the air when tubes
are broken. In all other cases it is assumed that discarded
equipment goes mainly to landfills. Minor amounts are volatilized
in fires or incinerators or lost by corrosion; lead-acid
batteries are recycled.

e. Includes solders, contacts, semiconductors
and other special materials (but not copper wire) used in
electrical equipment control devices. instruments, etc. Losses to
the environment are primarily via discard of obsolete equipment
to landfills. Mercury used in instruments is lost via breakage
and volatilization or spillage.

f. Chemical uses not embodied in final products
include catalysts. solvents, reagents, bleaches, etc. In some
cases a chemical is basically embodied but there are some losses
in processing. Losses in chemical manufacturing per se are
included here. Major examples include copper and mercury
catalysts (especially in chloride mfg); copper, zinc and chromium
as mordants for dyes; mercury losses in felt manufacturing;
chromium losses in tanning; lead in desulphurization of gasoline;
zinc in rayon spinning, etc. In some cases virtually all of the
material is actually dissipated. We include detonators such as
mercury fulminate and lead azide (and explosives) in this
category.

g. Chemical uses embodied in final products
other than paints or batteries include fuel additives (e.g. TEL).
anti-corrosion agents (e.g. zinc dithiophosphate), initiators and
plasticizers for plastics (e.g. zinc oxide), etc. Also included
are wood preservatives and chromium salts embodied in leather.
Losses to the environment occur when the embodying productivity
is utilized, for example gasoline containing TEL is burned and
largely (0.75) dispersed into the atmosphere. However, copper,
chromium, and arsenic are used as wood preservatives and and
dispersed only if the wood is later burned or incinerated. In the
case of silver (photographic film), we assume that 60 per cent is
later recovered.

h. Agricultural pesticides, herbicides, and
fungicides. Uses are dissipative but heavy metals are largely
immobilized by soil. Arsenic and mercury are exceptions because
of their volatility.

i. Non-agricultural biocides are the same
compounds, used in industrial, commercial, or residential
applications. Loss rates are high in some cases.

j. Medical/dental uses are primarily
pharmaceutical (including cosmetics) germicides, also dental
filling material. Most are dissipated to the environment via
waste water. Silver and mercury dental fillings are likely to be
buried with the dead body.

The term "emission coefficient," as
used in this context, means the fraction of the material in
question that is released in mobile form (to the air or water)
within a certain period (a decade, more or less). We exclude
wastes that are recycled or disposed of in landfills or in sludge
dumped offshore. We exclude toxic metals immobilized in clayey
soil. In a few cases we also include production-related losses
that were not included in the previous sections (e.g. process
wastes in the plating, tanning, and chemical industries). These
assumptions are obviously quite conservative, at least in the
sense that a case could be made for significantly higher
estimates of emissions.

It is unfortunate (and curious) that there are
almost no published data on emissions coefficients consumption
activities. Obviously, most analysts so far have not considered
such activities to be "sources" of pollutants. In the
absence of an existing body of literature (and of time to
undertake more intensive research on this topic ourselves) we are
led to a rather ad hoc choice of emissions coefficients. These
are displayed in table 8. Each coefficient represents the
fraction of total consumption in that category that is typically
unrecoverable in principle.

It should be emphasized that these estimates
are rather rough. In some cases, they are little better than
"guestimates." The results presented here, therefore,
are illustrative rather than authoritative. A task for the future
is to improve the approach, and particularly to make it more
relevant to major new policy initiatives.

In the case of tetra-ethyl lead (TEL) emissions
from gasoline consumption, it is probably not necessary to
compute emissions from an emission coefficient. Instead, on the
assumption that all lead in gasoline is eventually emitted, input
data on lead use as a gasoline additive should suffice. Such data
are available from the Bureau of Mines. To compute strictly
atmospheric emissions, however, the total lead used as a gasoline
additive should be multiplied by a factor of 0.75 to reflect the
fact that at least 25 per cent of the lead is trapped in the oil,
oil filters, or exhaust system of the cars and not emitted
directly to the atmosphere (Hirschler et al., 1957; Hirschler and
Gilbert, 1964).

It must be pointed out that, while the
numerical estimates in many cases are rather uncertain -
sometimes even by a factor of two or three there are only a few
important routes which clearly dominate the rest for each metal.

The next and last step is to allocate total
domestic usage of each of the eight metals among the ten
categories over the past 100 years. The allocation among uses has
been far from unchanging. Many formerly important uses have
disappeared, while others have emerged as recently as the last
decade. Consumption data by use are available, in general, only
since the Second World War. For earlier periods one must rely on
a scattering of real data supplemented by a variety of other
clues.

Our composite picture of historical heavy
metals usage patterns for the United States is summarized in
tables A-H in the Appendix. Each table represents one metal, and
is arranged as follows:

1. Percentage of metal use by consumptive
category.

2. Consumption in metric tons (US).

3. Emissions due to consumptive use (US).

The Appendix also includes a final summary
table (table I) of productionrelated and consumption-related
emissions, and the consumption-related fraction, for seven of the
eight metals (excluding silver, for which productionrelated
emissions data are not available). The consumption fraction,
expressed as a percentage, is plotted for two groups of metals in
figure 1.

As noted already, the major results of our
analysis are summarized in tabular form in the Appendix (see
tables A-H).

The lower part of figure 1 displays, for
chromium and copper, the ratio of consumption-related dissipative
losses to production-related emissions (not including losses at
the mine) in each decade. For these two metals, whose major uses
are in metallic form or, in the case of chromite, as bricks for
blastfurnace liners, production-related emissions are still
dominant, but the consumption share is increasing steadily.

In the upper part of figure 1 the same data are
shown for five other toxic heavy metals: arsenic, cadmium, lead,
mercury, and zinc.

In two cases, arsenic and mercury, the
consumption share has always been high. Arsenic has been used
(until very recently) almost exclusively because of its biotoxic
properties. Such uses are inherently dissipative. This is also
partly true for mercury. For instance, mercury is the basis of a
number of commercial fungicides, germicides, and preservatives.
The major dissipative uses of cadmium, in the past, were in
pigments and as a contaminant of zinc oxide used in tyres. The
use of cadmium for red and orange pigments has declined sharply,
while metallic usage (mainly in batteries) has increased even
more sharply. This accounts for the inverted "U" shape
of the cadmium curve. (As electronic uses of arsenic, in gallium
arsenide, may grow in the future, a similar downturn may be
expected in the future.)

The increasingly dissipative usage of lead is
only partly due to its role as a gasoline additive (largely
phased out since 1980, of course). In earlier decades lead was
the basis of one of the most widely used agricultural
insecticides (lead arsenate). In the nineteenth and early
twentieth century, lead was also extensively used as a white
pigment for oil-based paints. So-called white lead was later
replaced by a zincbased white pigment (lithopone), which was
subsequently replaced by the white pigment now used most widely,
titanium dioxide. Red lead was the major metal-protective paint
until the last decade or so. The yellow paints currently used on
roadways and to protect heavy machinery - such as bulldozers -
are largely chromium-based, which accounts in part for the rapid
rise in dissipative uses of chromium. Zinc is also used in large
quantities in tyres and paper.

As we indicated at the outset, for three of
these five metals investigated the dissipative
consumption-related emissions far outweigh the production-related
emissions; in fact the consumption shares for arsenic, lead, and
mercury are close to 100 per cent. In the case of zinc, that
share is rising rapidly; for cadmium the consumptive share is
still about 50 per cent of the total.

One of the eight metals included in the study
was silver. Production-related emissions data are non-existent.
However, since silver is a rather valuable metal, and since
almost all of it is now obtained as a by-product of lead, zinc,
or copper smelting and refining, one could probably argue that
productionrelated emissions are essentially non-existent. On the
other hand, one major consumptive use of silver is still in
photography. While commercial photographic studios do recycle
some silver, a significant fraction is lost. Thus, for silver,
too, the consumption-related share of total emissions is probably
close to 100 per cent.

The foregoing analysis was entirely historical.
But one or two points worth considering for the future emerge
clearly. One of them is the fact that several of these toxic
heavy metals play a major and increasing role in electronics.
These include lead (solder), arsenic (semi-conductors), cadmium
(batteries), mercury (switches and batteries), and silver
(batteries and connectors). Electronic wastes are accumulating in
obsolete equipment at an enormous rate in the United States, and
all around the world. Much of this electronic "junk"
might be dumped in landfills in future years, and some will be
inadvertently incinerated. Many states already classify such
wastes as hazardous. Leaching - especially that due to
increasingly acid rainfall and combustion will mobilize some of
these toxic materials. There is, therefore, a strong need for
more research on ways and means of closing the materials cycle.